Keypad signal input apparatus

ABSTRACT

Keypad apparatus for registering signals corresponding to data that a user enters by pressure on keys of an array in a surface extending in two dimensions. The elements of first and second sets of impedance elements (R) are connected in series through respective interconnections and a signal processor applies first and second reference signals across the first and second sets of impedance elements respectively. User pressure on the keys makes or breaks connections through corresponding contact elements between a respective pair of the interconnections, one from the first set of impedance elements and one from the second set of impedance elements, so as to generate first and second output signals (PX 1 , PY 1 ) that together are a corresponding combination of the first and second reference signals that is unique to the actuated key elements.

FIELD OF THE INVENTION

This invention relates to keypad apparatus for registering signalscorresponding to data that a user enters by pressure on discretefeatures of a surface extending in two dimensions and to data entryapparatus including such keypad apparatus.

BACKGROUND OF THE INVENTION

Keypads are used in various devices, including portable telephones andpersonal digital assistants (‘PDAs’) for example. The discrete featuresthat the user presses to enter data may take various forms, such aspush-buttons projecting through the surface or elastic relief on thesurface, for example. The number of features will depend on theapplication that the keypad is used for but typically is of the order of20 to 40, for example 28 if the features form a 4 by 7 array.

The keypad generates electrical signals, which are then processed by asignal processor. Typically, the signal processor has a limited numberof input pins available for each input or output device to which it isconnected. This is especially the case if the signal processor isintegrated with an applications processor providing applicationprogrammes for the user, which is desirable, since such a configurationoffers advantages such as fast reaction times in addition to reducedpackage size.

Another type of data entry apparatus is a touch panel or touch screen,in which a two-dimensional surface is sensitive to the position at whicha user touches the surface using a pointed object such as a stylus orhis finger, for example. A touch screen may simultaneously display animage produced by the device and the device reacts to the position atwhich the user touches the surface relative to the displayed image. Thepositional sensitivity of the screen or panel to the touch isessentially continuous, unlike a keypad, the discrete features of whichare discontinuous. The touch screen or panel also requires input pins ata signal processor. Touch screens and panels find wide application.However keypads also find wide application both for cost reasons, ifthey are used instead of touch panels, and for ergonomic reasons, sincethey provide a simple and easy way of entering alphanumeric data.

It is desirable to limit the overall number of input pins required atthe signal processor, for example to avoid increasing its package sizeand die size in the case of an integrated circuit processor. It is alsodesirable to limit the number of different signal processors.

SUMMARY OF THE INVENTION

The present invention provides keypad apparatus and data entry apparatusas described in the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a known keypad;

FIG. 2 is a diagram of a known resistive touch screen and signalprocessor;

FIG. 3 is a diagram of keypad apparatus in accordance with oneembodiment of the invention, given by way of example;

FIG. 4 is a diagram of the keypad apparatus of FIG. 3 and signalprocessor in operation sensing X-coordinates of an actuated key;

FIG. 5 is a diagram of the keypad apparatus of FIG. 3 and signalprocessor in operation sensing Y-coordinates of an actuated key;

FIG. 6 is a plan view of a jog-pad module for use with the keypadapparatus of FIG. 3,

FIG. 7 is a diagram of the keypad apparatus of FIG. 3 with two keysactuated,

FIG. 8 is a schematic diagram of a three-dimensional switch element in apreferred embodiment of the invention, given by way of example;

FIG. 9 is a schematic diagram of one form of actuation of thethree-dimensional switch element of FIG. 8;

FIG. 10 is a schematic diagram of another form of actuation of thethree-dimensional switch element of FIG. 8; and

FIG. 11 is a schematic diagram of resistor networks used in keypadsincorporating the three-dimensional switch elements of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The keypad shown in FIG. 1 comprises an array of keys or push-buttonswitches 1 each comprising a button 2 projecting through atwo-dimensional surface (not shown) and bearing an electrical connectionelement 3. The keypad also comprises column leads 4 and row leads 5, theswitches 1 comprising contact elements 6 connected to individual columnleads and contact elements 7 connected to individual row leads. The key1 is biased mechanically away from the contact element 6 and 7 butconnects the contact elements 6 and 7 electrically when actuated by auser pushing the button 2. Connection in this way of the contactelements 6 and 7 of any given push-button switch 1 makes a respectiveunique connection between a column lead 4 and a row lead 5.

Each column lead 4 has a corresponding column terminal 8, and each rowlead 5 has a corresponding row terminal 9. In this example of a keypad,the array of switches 1 comprises 4 columns and 7 rows, so that thereare a total of 11 terminals to be connected to respective pins on asignal processor circuit (not shown). It is desirable to reduce thenumber of pins to which the keypad must be connected.

FIG. 2 shows another data entry apparatus, comprising a touch panel 10.Touch panels are well-known in the art and the touch panel illustratedis of the kind comprising an upper resistive layer 11 and a lowerresistive layer (not shown), which are spaced apart by an electricallyinsulating system which allows the upper and lower layers to makelocalised contact with each other when a pointed object such as a stylusis pressed at a point on the upper surface 11 by the user. Electricalconnection is made to opposite edges of the upper resistive layer 11 byspaced X-electrodes 12 and 13 and to opposite edges of the lower layer,orthogonal to the electrodes 12 and 13, by Y-electrodes 14 and 15.

The touch panel 10 is connected to an analogue signal processor module16. The electrode 12 is connected to a pin PX1 of the processor 16 andthrough a resistor Rpd to a reference voltage force DVDD. The electrode13 is connected to a pin PX2 of the processor 16. The electrodes 14 and15 are connected to pins PY1 and PY2 respectively of the processor 16. Apin R1A of the processor 16 is connected through a resistor Rpu toground and through a resistor Rp1 to a pin R1B of the processor. A pinR2A of the processor is connected through a resistor Rp2 to a pin R2B ofthe processor.

The energisation and detection of the touch screen 10 is controlled byinternal switches SW1 to SW8 of the processor. In more detail, oneterminal of the switch SW1 is connected to the reference voltageterminal DVDD and its other terminal is connected to the pin PY1. Oneterminal of the switch SW2 is connected to the pin PY1 and the otherterminal is connected to the pin R1A. One terminal of the switch SW3 isconnected to the reference voltage terminal DVDD and its other terminalis connected to the pin PX1. One terminal of the switch SW4 is connectedto the pin PX1 and the other terminal is connected to the pin R1A. Oneterminal of the switch SW5 is connected to the pin R2B and its otherterminal is connected to the pin PY2. One terminal of the switch SW6 isconnected to the pin PY2 and its other terminal is connected to ground.One terminal of the switch SW7 is connected to the pin R2B and its otherterminal is connected to the pin PX2. One terminal of the switch SW8 isthe connected to the pin PX2 and its other terminal is connected toground. The pins RIB and R2A are connected to the positive and negativeinputs of the analogue to digital converter 17 that converts theanalogue signals at its inputs to digital signals at its outputs 18 and19.

In operation, the voltage level of PX1 is monitored to detect a paneltouch. While in the idle mode, the pin PY2 is connected to GND, whilePX1 is pulled-up to DVDD by the resistor Rpd. When the panel is touched,the PX1 input is pulled towards ground through the touch screen and PY2.This produces a falling edge and triggers a panel touch detectioninterrupt.

The subsequent sequence of operation of the switches is automaticallygenerated once an interrupt signal is generated in response to the usertouching the upper layer, the analogue signals measured at theelectrodes being applied to an analogue to digital converter 17 in theprocessor 16, which generates digital output signals at output terminals18 and 19. The processor 16 applies a voltage alternately across thepair of electrodes 12 and 13 and across the pair of electrodes 14 and15, and responds to the voltage at the other electrode pair. Inoperation, localised contact at a point on the touch screen produced bythe user touching the upper layer 11 causes the upper layer and lowerlayer of the touch panel 10 to present voltage dividers when a voltageis applied across either pair of the electrodes 12, 13 or 14, 15, theresistance ratio of the voltage divider defining the position at whichthe upper layer 11 is touched.

FIG. 3 shows keypad apparatus in accordance with one embodiment of thepresent invention. Elements which are similar to the keypad of FIG. 1bear similar reference numerals. However, the keypad apparatus 1 of FIG.3 only requires connection to four input-output pins of a signalprocessor. The keypad apparatus 1 of FIG. 3 comprises a first set ofidentical impedance elements 20 and a second set of identical impedanceelements 21 that are connected to the signal processor. The impedanceelements of the sets 20 and 21 are connected together and to the ends ofthe sets through respective interconnections. In the preferredembodiment of the invention, the impedance elements of the sets 20 and21 are resistive elements R. In another embodiment of the invention, theimpedance elements are capacitive elements, the keypad apparatus beingfed by a sinusoidal voltage supply instead of the direct referencevoltage at terminal DVDD.

In the embodiment of the invention shown in FIG. 3, the signal processorfor the keypad is a processor 16 like that shown in FIG. 2. As shown inFIG. 4, the column leads 4 are connected to respective interconnectionsof the set 20 (including interconnections at the ends of the set) andthe row leads 5 are connected to respective interconnections of theimpedance element set 21. One end interconnection of the set 20 isconnected to the pin PY1 and the other end interconnection is connectedto the pin PY2. One end interconnection of the set 21 is connected tothe pin PX1 and the other end to the pin PX2.

It will be appreciated that the connection of the array of keys 1 to thesets 20 and 21 of impedance elements enables the keypad apparatus toemulate a touch panel. In particular, pressing one of the keys 1 makesconnections between a respective unique combination of theinterconnections in the sets of impedance elements 20 and 21 through itscontact elements 6 and 7. When one of the pairs of pins PX1, PX2 or PY1,PY2 is energised while one of the keys 1 is pressed, output signals aregenerated that are a corresponding unique combination of the referencevoltage DVDD applied across the sets of impedance elements 20 and 21,which act as respective voltage dividers whose division ratios depend onwhich column and row lead 4 and 5 is activated by the selected key 1.

A measurement of the X-position of the actuated key switch 1 is made byclosing switch SW2 to connect the PY1 input to the ADC 17, by closingswitch SW3 to apply DVDD to PX1 and closing switches SW7 and SW8 toconnect PX2 and R2B to ground, as shown in FIG. 4. The other switchesSW1 and SW4 to SW6 are open, so that the pin PY2 and correspondinginterconnection of the set 20 of impedance elements is floating. Thevoltage appearing at the pin PY1 is then applied through pin R1A,resistor Rp1 and pin RIB to the positive input of the A/D converter 17,whose negative input is connected to ground through pin R2A, resistorRp2 and pin R2B.

The voltage measured is determined by the voltage divider developed inthe set 20 of impedance elements by the actuated switch 1 betweendivided values illustrated as RX1 and RX2. For this measurement, theY-divider resistance RY1 does not affect the conversion due to highinput impedance of the A/D converter.

Voltage is then applied to the other axis to measure the Y-position ofthe actuated key switch 1 by closing switch SW4 to connect the PX1 inputto the ADC 17, by closing switch SW1 to apply DVDD to PY1 and closingswitches SW5 and SW6 to connect PY2 and R2A and R2B to ground, as shownin FIG. 5. The other switches SW2, SW3, SW7 and SW8 are open, so thatthe pin PX2 and corresponding interconnection of the set 21 of impedanceelements is floating. The voltage appearing at the pin PX1 is thenapplied through pin R1A, resistor Rp1 and pin RIB to the positive inputof the A/D converter 17, whose negative input is connected to groundthrough pin R2A, resistor Rp2 and pin R2B.

The measurements of the X- and Y-axes continue to be made alternately.

With equal values for each of the impedance elements of the sets 20 and21, examples of the relative voltages measured for actuation of any oneof the keys illustrated in FIG. 3 is shown below. Keys X Y AA 0 0 AB 00.6 AC 0 1.2 AD 0 1.8 BA 0.3 0 BB 0.3 0.6 BC 0.3 1.2 BD 0.3 1.8 CA 0.6 0CB 0.6 0.6 CC 0.6 1.2 CD 0.6 1.8 DA 0.9 0 DB 0.9 0.6 DC 0.9 1.2 DD 0.91.8 EA 1.2 0 EB 1.2 0.6 EC 1.2 1.2 ED 1.2 1.8 FA 1.5 0 FB 1.5 0.6 FC 1.51.2 FD 1.5 1.8 GA 1.8 0 GB 1.8 0.6 GC 1.8 1.2 GD 1.8 1.8

It will be noted that there is a difference of 0.3 volts between thediffering coordinates of any two adjacent keys. This enables the keys tobe readily distinguished and identified by the analogue to digitalconverter 17.

Further functions can be obtained with the addition of a “jog pad”module, illustrated in plan view in FIG. 6, which is particularly usefulwhen playing certain games associated with the control of moving images,for example. The jog pad enables a disk shaped pad to be rocked forwardsand backwards or left and right to actuate any one of four adjacentkeys, but also to be rocked diagonally to actuate two adjacent keys 1simultaneously. It is also possible to actuate two adjacent keysdirectly in the absence of such a jog pad.

The operation of the key pad apparatus of FIG. 3 corresponding tosimultaneous actuation of two keys BB and BC in the same row isillustrated in FIG. 7 and corresponds to short-circuiting of theimpedance element RA of the set 20 that both of the actuated keys areconnected to. Typical voltages resulting from the simultaneous actuationof two keys in the same row or column are illustrated in the tablebelow. Keys X Y BB & BC 0.3 0.9 BB & CB 0.36 0.6 CB & CC 0.6 0.9 CC & BC0.36 1.2 CB & CC 0.6 0.9 CB & DB 0.72 0.6 DB & DC 0.9 0.9 DC & CC 0.721.2

It will be seen that intermediate coordinate values are obtained fromthe simultaneous actuation of two keys in the same row or column whichare readily distinguishable from any other coordinate values obtained bypressing one or two keys, the values of the other coordinate (column orrow) differing only within the normal margin of error, due to the highinput impedance of the ADC17.

In a preferred embodiment of the invention illustrated in FIG. 8, atleast some of the keys 1 comprise further Z-node contact elements suchas 22, 23 and 24 with which the conducting element 3 of the key may makecontact while maintaining contact with the contact element 6 and 7 ofthe X-node and Y-node. The Z-node contact elements 22 to 24 are spacedapart perpendicularly beneath the keypad surface so that as the key 1 isprogressively depressed further, it selectively contacts the contactelements 22 to 24 in succession.

As shown in FIG. 9, in one embodiment of the invention, the electricalconnecting element 3 makes a connection between the contact elements 6and 7 of the X-node and Y-node and simultaneously makes a connectionwith the selected contact element 22 to 24 of the Z-node. In analternative embodiment shown in FIG. 10, the electrical connectingelement 3 makes a connection between the contact elements 6 and 7 of theX-node and Y-node and a further connection member 3A makes a connectionbetween the selected contact element 22 to 24 of the Z-node and one ofthe contact elements 6 and 7, in the example illustrated the contactelement 6 of the Y-node, electrical connection with the other electricalcontact element, in this case the contact element 7 of the X-node beingmade through the connecting element 3.

As shown in FIG. 11, a set of impedance elements 25 is provided for theZ-contact elements such as 22 to 24, comprising interconnected impedanceelements similar to those of the sets 20 and 21. The contact elementssuch as 22 are connected through Z-leads 26 to respectiveinterconnections of the set 25 and the contact elements such as 23 and24 are connected by respective Z-leads to other interconnections of theset 25.

Accordingly, in this embodiment of the invention, each key a has aunique X and Y position with corresponding unique combination ofelectrical connections to the impedance element sets 20 and 21, and aplurality of Z-nodes for different positions transversely to the surfaceof the keypad. Thus the switch position is identified by its electricalX, Y and Z co-ordinates. In operation, the cycle of measurement of theco-ordinates alternates between the sets 20, 21 and 25. When a key α isdepressed, X_(α), Y_(α) and Z_(α) are connected together. Voltage isfirst applied across the set 21 of impedance elements to measure the Xco-ordinates and the voltage is sensed on the pin PY1. Next the voltageis applied across the set 20 of impedance elements and the voltage atthe pin PX1 is measured, corresponding to the Y co-ordinates. Lastly,the voltage is applied across the set 25 of impedance elements and thevoltage is again measured on pin PY1 to measure the Z co-ordinates ofthe key.

It will be appreciated that such three dimensional keys are particularlyvaluable in a joystick module, utilising 4 or 8 adjacent keys that arethree dimensional as described above, since the different Z positions ofthe keys multiply the number of different possible combinations ofpositions of the joystick that can be sensed.

The keypad apparatus and signal processor described above may be usedinstead of a touch panel or touch screen in a device such as a portabletelephone or personal digital assistant. In one embodiment of theinvention, the keypad such as shown in FIG. 3 may be disconnected fromthe signal processor 16 and a resistive touch screen or other touchpanel connected in its place, offering an alternative data entry foralternative uses of the device. In a preferred embodiment of theinvention, the device includes both the keypad and a resistive touchscreen, with a multiplex device (not shown) to connect the signalprocessor 16 alternatively to the resistive touch screen or the keypad.In this way, a single signal processor may be used for both the dataentry modules.

With the embodiments of the invention shown in the accompanyingdrawings, no extra input-output pins are required on the signalprocessor 16. The provision of the sets of impedance elements 20, 21 and25 may be provided in a small and inexpensive package, especially whereresistive elements are used as described. Only 4 line connectors areneeded between the keypad of FIG. 3 and the signal processor 16, in thecase of the two dimensional keypad.

The operation of the signal processor 16 has been described with the useof direct reference voltages applied in alternation in time to therespective sets of impedance elements to measure the position of theactuated key in different co-ordinates. In another embodiment of theinvention, alternating reference voltages of different frequencies areapplied simultaneously to the different sets of impedance elements andthe co-ordinate positions are measured simultaneously, the signalprocessor 16 distinguishing the measured co-ordinates by the frequency.

1. Keypad apparatus for registering signals corresponding to data that auser enters by pressure, comprising: a surface extending in twodimensions; first and second sets of impedance elements, the elements ofeach set being connected in series through respective interconnections;reference signal means for applying first and second reference signalsacross said first and second sets of impedance elements respectively;and an array of discrete key elements juxtaposed with said surface andselectively actuable by user pressure on said features to make or breakconnections through corresponding contact elements between a respectivepair of said interconnections, one from said first set of impedanceelements and one from said second set of impedance elements,characterised by said reference signal means is arranged to apply saidreference signals alternately across said first set and across saidsecond set of impedance elements, so as to generate first and secondoutput signals that together are a corresponding combination of saidfirst and second reference signals that is unique to the actuated keyelements, and output means responsive to said output signals, saidoutput means comprising digital-to-analogue converter means common tosaid first and second output signals.
 2. Keypad apparatus as claimed inclaim 1, wherein said reference signals are respective direct voltagesand said impedance elements present electrical resistances.
 3. Keypadapparatus as claimed in claim 1 or 3, wherein said array of discrete keyelements comprises a two-dimensional array of switches disposed at saidsurface for actuation by the user and connected with respective pairs ofsaid interconnections.
 4. Keypad apparatus as claimed in claim 3,wherein said array of discrete key elements is an orthogonal array. 5.Keypad apparatus as claimed in claim 3, and comprising; a third set ofsaid impedance elements connected in series through respectiveinterconnections, said reference signal means being arranged to applythird reference signals across said third set of impedance elements, atleast some of said key elements comprising a three-dimensionaldisposition of said electrical contact elements said features beingprogressively movable transversely to said surface by user pressure tomake or break connections through corresponding contact elements betweenan interconnection from said first set of impedance elements, aninterconnection from said second set of impedance elements and also arespective interconnection from said third set of impedance elementsselected by the degree of user actuated movement of the key, so as togenerate first, second and third output signals that together are acorresponding combination of said first, second and third referencesignals that is unique to the actuated contact elements.
 6. Keypadapparatus as claimed in any preceding claim 5 wherein simultaneousactuation of adjacent ones of said discrete key elements is arranged togenerate first and second output signals that are a correspondingcombination of said first and second reference signals unique to thesimultaneously actuated key elements.
 7. Keypad apparatus as claimed inclaim 5, wherein said output means includes analogue to digitalconverter means responsive to analogue values of said output signals togenerate digital output signals.
 8. Keypad apparatus as claimed in claim5, wherein said reference signal means is arranged to apply saidreference signals alternately across said first set and across saidsecond set of impedance elements, so as to generate said first andsecond output signals alternately.
 9. Keypad apparatus as claimed inclaim 8, wherein said reference signal means is responsive to actuationof a discrete key element to trigger application of said referencesignals alternately across said first and second sets of impedanceelements.
 10. Keypad apparatus as claimed in claim 9, wherein saidreference signal means is responsive to actuation of a discrete keyelement to generate a trigger signal, said reference signal meansincluding signal processing means responsive to said trigger signal forprocessing said output signals.
 11. Keypad apparatus as claimed in claim9, wherein said first and second sets of impedance elements areconnected between first and second pairs of terminals respectively, saidreference signal means is arranged to apply said reference signalsalternately across said first and second pairs of terminals, and saidoutput means is responsive to said output signals appearing at least oneof said terminals to which said reference signals are not being applied.12. Data entry apparatus comprising keypad apparatus as claimed in claim5 and further comprising a touch panel apparatus comprising first andsecond juxtaposed impedance layers presenting distributed impedances,first and second pairs of electrodes coupled with respective pairs ofopposed edges of said impedance layers, and connection means forselectively operably connecting said reference signal means and saidoutput means with said sets of impedance elements of said keypadapparatus or with said pairs of electrodes of said touch panelapparatus.